The present invention relates generally to air bag systems for use as safety devices in automotive vehicles and, more particularly, to a non-inverting dual voltage regulation set point power supply using a single inductor for a restraint control module.
Over the past several years, there has been a trend in the automotive industry to install air bag systems in vehicles to enhance protection traditionally afforded vehicle occupants through the use of seat belts. In some automotive vehicles, the inflatable restraint system may be an air bag system disposed within an occupant compartment in the automotive vehicle in close proximity to either a driver occupant or one or more passenger occupants. Usually, the air bag system includes a restraint control module that is connected to the vehicle structure and an air bag for deployment through an opening in a cover to extend and inflate in an occupant compartment of the automotive vehicle. The deployed air bag restrains movement of the occupant to protect the occupant from forcefully hitting parts of the automotive vehicle as a result of an automobile accident.
Air bag systems typically include a restraint control module, a reaction canister and an air bag and inflator that are stored inside the reaction canister. Generally speaking, the inflator is actuated by a signal received from a vehicle deceleration sensor or accelerometer that is connected to the restraint control module, which, in turn, causes a discharge of inflator gas into the interior of the air bag. The restraint control module controls the overall operation of the air bag system and essentially could be viewed as the main control unit for the air bag system.
As with any system based on electronic components and sensors, air bag systems and their associated electronic components, require power from a power supply in order to function properly. During normal operation, the power used to drive an air bag system and its related components originates from a battery that is located in the automotive vehicle. However, the voltage provided by the battery can often vary dramatically during operation depending on various load conditions as well as the operating conditions of the automobile. As such, a need exists to provide certain components and sensors of an air bag system with a regulated voltage supply that is capable of providing power to various components of the air bag system.
The present invention discloses a non-inverting dual voltage regulation set point power supply that is preferentially used in a restraint control module of an automobile air bag system. The non-inverting dual voltage regulation set point power supply includes a main power source, which originates from an automobile battery in the preferred embodiment. A regulated voltage generation circuit is connected with the main power source, which generates a regulated output voltage with a predetermined upper set point and a lower set point. A buck switch is connected to the main power source and the regulated voltage generation circuit. The buck switch causes the regulated output voltage generated by said regulated voltage generation circuit to be set at the upper set point if the voltage supplied from the main power source is greater than the upper set point or track the input power from the main power source for voltages exceeding the lower set point and below the upper set point. A boost switch is connected with the regulated voltage generation circuit for boosting the regulated output voltage generated by the regulated voltage generation circuit to the lower set point if the voltage supplied from the main power source is less than the lower set point.
In the preferred embodiment of the present invention, the non-inverting dual voltage regulation set point power supply further includes a buck gate driver that is connected to gate of the the buck switch. The buck gate driver controls the switching operation of the buck switch such that the buck switch regulates the regulated output voltage at the upper set point during periods in which the input voltage from the main power source is greater than the upper set point. The preferred buck switch is a DMOS transistor, which is preferentially a field-effect transistor (FET).
The non-inverting dual voltage regulation set point power supply also includes a boost gate driver connected to the gate of the boost switch. The boost gate driver controls the switching operation of the boost switch such that the boost switch regulates the regulated output voltage at the lower set point if the voltage from the main power source is below the lower set point. The preferred boost switch is also a DMOS transistor, which is also preferentially a FET.
A regulation control circuit is connected to the buck gate driver and the boost gate driver. The regulation control circuit is used to selectively drive the buck gate driver and the boost gate driver to maintain the regulated output voltage between the upper set point and the lower set point. In the preferred embodiment, the regulation control circuit comprises a pair of error amplifiers connected to a pair of pulse width modulation comparators. A voltage feedback circuit is connected to the regulated output voltage and the regulation control circuit. The preferred voltage feedback circuit includes a voltage divider circuit that has a plurality of resistors.
The regulated voltage generation circuit comprises an inductor connected with a capacitor. The use of a single inductor minimizes parts by sharing the inductor for both buck and boost operations. It also provides lower inductor ripple (lower EMI) and allows for the use of a smaller sized inductor, thereby providing further cost benefits over prior systems.